Gilbert damping of CoFe-alloys

We report structural, magnetic and dynamic properties of polycrystalline Co_xFe_1−x-alloy films on Sapphire, Silicon, and MgO substrates across the full composition range, by using a vector network analyser ferromagnetic resonance measurement technique (VNA-FMR), superconducting quantum interference device magnetometry (SQUID) and x-ray diffraction (XRD). In the approximate vicinity of 28% Co, we observe a minimum of the damping parameter, associated with a reduction in the density of states to a minimum value at the Fermi energy level. For films on all substrates, we find magnetic damping of the order of 4–5 · 10⁻³, showing that the substrate does not play a major role. Using a post-annealing process, we report a decrease of the magnetic damping down to 3–4 · 10⁻³. We find that the saturation magnetization depends approximately reciprocally on the damping parameter with varying alloy composition. (paper)